An ink jet printer of the type frequently referred to as drop-on-demand, has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of channels. Piezoelectric devices or power pulses cause the droplets of ink to be expelled as required, from orifices or nozzles located at the end of the channels. In thermal ink-jet printing, the power pulses are usually produced by resistors, also known as heaters, each located in a respective one of the channels. The heaters are individually addressable to heat and vaporize the ink in the channels. As a voltage is applied across a selected heater, a vapor bubble grows in that particular channel and ink bulges from the channel nozzle. At that stage the bubble begins to collapse. The ink within the channel then retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel nozzle and towards the recording medium whereupon hitting the recording medium a spot is formed. The channel is then refilled by capillary action which, in turn, draws ink from a supply container of liquid ink. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774.
The ink jet printhead may be incorporated into a carriage type printer or a page width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles) at a time on a stationary recording medium, such as paper or a transparency.
After the swath is printed, the paper is stepped a distance equal to the height of a printed swath or a portion thereof, so that the next printed swath is overlapping or contiguous therewith. The procedure is repeated until an entire page is printed. In contrast, the page width printer includes a stationary printbar having a length equal to or greater than the width of the paper. The paper is continually moved past the page width printbar in a direction substantially normal to the printbar length and at a constant or varying speed during the printing process. Because the printbars have an arrangement of linearly aligned nozzles, the alignment of the printbar with respect to the recording medium is critical.
Printers typically print information received from an image output device such as a personal computer. Typically, these output devices generate pages of information in which each page is in the form of a page description language. An electronic subsystem (ESS) in the printer transforms the page description language into a raster scan image which is then transmitted to a peripheral or image output terminal (IOT). The raster scan image includes a series of scan lines in which each scan line contains information sufficient to print a single line of information across a page in a linear fashion. In the page description language, printed pages also include information arranged in scan lines.
In printbars which print a single line of pixels in a burst of several banks of nozzles, each bank printing a segment of a line, the banks of nozzles are typically fired sequentially and the nozzles within a bank are fired simultaneously. An ink let printbar having banks of nozzles is described in U.S. Pat. No. 5,300,968 to Hawkins incorporated herein by reference. These printbars include a plurality of printhead dies, wherein each die prints a portion of a line. Within the die, the banks of nozzles print a segment of the portion of the line. Such printbars must be precisely oriented with respect to the process direction so that the printing of a last portion of a line, which is delayed in time from the printing of a first portion of a line, results in a line of pixels that is collinear. To accomplish acceptable printing using this type of printbar, the printbar is not aligned exactly perpendicular to the process direction, but is instead tilted slightly with respect to the process direction. This means that each die prints a portion of a different scan line.
Many printing devices such as xerographic printers having a laser raster output scanner can use information in raster scan format to print the image without performing any manipulation on the image data received. The architecture of a page width printbar is not, however, quite so accommodating. Since the printbars are slightly angled with respect to the process direction to compensate for the sequential firing of banks of nozzles, the output of any raster output device must be manipulated before printing can occur. Consequently, the raster data to be printed on a thermal ink jet page width printbar must undergo some transformation. It is therefore important that the transformation be done in a timely manner. Historically, the necessary data manipulation was done with software. Software processing performed the transformations before the data was shipped to the printbar. These processes, however, are time consuming and not very efficient.
Various printers and methods for manipulating image data for printing on a recording medium are illustrated and described in the following disclosures which may be relevant to certain aspects of the present invention.
U.S. Pat. No. 4,779,105 to Thomson et al. describes a printer interface for a non-impact printing apparatus and more particularly to apparatus which converts originating image data into output image data and a raster scan arrangement suitable for presentation to a printing subsystem.
U.S. Pat. No. 5,016,190 to Thomson describes a method and apparatus for converting data representative of a plurality of cells arranged independently of one another on a page into data in raster scan order for subsequent printing. Cell data for individual cells is fetched in an order dependent on the line of raster scan where the cell first appears and the bit position for the first bit representing the cell.
U.S. Pat. No. 5,084,831 to Morikawa et al. describes a printer having a memory for storing dot image data to be printed. The printer prints in two modes, the first mode being a full bit map mode for storing a page of data and a second strip map mode for a smaller amount of data than a page of data. In the full bit map mode, the bit data is sent to the printer after all the bit data of a page has been stored in the bitmap memory. In the strip map mode, an image of one page is divided into a plurality of image portions and the bit data is written/read to and from the bit map memory in the unit of the image portion.
U.S. Pat. No. 5,108,207 to Isobe et al. describes a printer with a variable memory size. The printer includes a memory unit having a first memory area for storing input data and a second memory area for storing image data obtained by developing input data. The first memory area and the second memory area are arranged within the same memory space to form the memory unit. An area control unit changes a proportion of the capacity of the second memory area within the memory unit to alter the relative proportions of the first memory area and the second memory area in the memory space forming the memory unit.